The new find, UGPS 0722-05, is less than 10 light years from here. But
sky-watchers missed it for so long because it’s a brown dwarf, a member
of the murky class of celestial objects that linger between gas giant
planets and low-mass stars. Brown dwarfs have so little mass that they
never get hot enough to sustain the nuclear fusion reactions that power
stars like the sun. Still, they do shine, because they glow from the
heat of their formation, then cool
and fade.

This dwarf’s temperature is somewhere between 266 and 446 degrees
Fahrenheit, making it the coldest scientists have even seen. With its
minimal activity, the brown
dwarf gives off just 0.000026 percent the amount of light that our
sun does.

Unassuming Generally Puny Star #0722-05 is particularly interesting because of its implications for the total number of stars in the universe as well as its proximity. If we missed it we may have missed others fairly close as well.

While even the much closer Proxima Centauri is well beyond our reach the possibility of nearby stars is of more than passing interest.

Nemesis, is a star hypothesized to be a companion to our own sun. There has, over the last few years been some indirect evidence in support of its existence. One theory astronomers had to explain its not being discovered yet was that it was a very dim red dwarf that had not had an accurate parallax measurement taken and whose brightness was overestimated contributing to its position being assumed to be much farther out.

This discovery makes it quite plausible that there is another star in our solar system that we simply haven't seen at all yet.

Science Babe is Maya from Sunshine Sketch...and an example of poor casting in this role.

1
I'm extremely skeptical about the Nemesis proposal. The difficulty is that the orbital period they hypothesize, measured in tens of millions of years, is only possible if Nemesis is really far out there, light years away. The problem is that I don't believe it could remain gravitationally bound to Sol over the course of hundreds of millions of years if it was that far out. Stars move. The galaxy rotates. We currently are in a relatiely sparse part of the spiral arm, but we've been in busy areas in the past. And there's just too many chances for gravitational encounters with other stars over a period of time that long which would break Sol's orbital hold on Nemesis and toss it out to orbit the galaxy directly.

2
Actually the distance given for the hypothetical star is anywhere from .33 Light years to two LY so it could be held on to by the sun. But you're right that would involve far too short a "year" for the 26 million yea cycle. It is also possible that it is in a weird orbit like Cruithnes association with Earth and only crosses the Oort cloud after hundreds or thousands of orbits.

Even if there is a second star in our Solar System (and there is superficial evidence that there might well be). It doesn't necessarily mean the Nemisis hypothisis is true. The supposed periodicity could be nothing more than pattern spotting or it could be due to our orbit on the galactic plane. Alternatively extinctions are due due to Hikari, Akari and two robots doing a controlled burn every 26 million years....but that show was a case study in fail so we'll just dismiss that possibility for now.